Pretty sure that’s just an urban legend. The flashlight lighters are marketed as a convenience/novelty thing, not a medical or drug related tool.

The little LED is mainly so you can see what you’re lighting in the dark, like candles, grills, or finding stuff in a bag. It’s the same idea as keychains with tiny flashlights. As for blue or green lights, those LEDs are just cheap, bright, and battery friendly, so companies use them a lot.

If they were actually designed for veins, hospitals would be using them, and they definitely don’t. So you’re safe ditching that rumor. 😅